1. Field of the Invention
The present invention relates to a method and a device that extract a clock signal from a light signal. Particularly, the invention relates to the method and the device that are capable of extracting clock signals from light signals according to a plurality of light signals with different bit rates.
2. Description of Related Art
Conventionally, the type of a bit rate of a light signal that transmits through an optical communication network is fixed to one type in advance. An optical transmitting/receiving device, a route switching device, a light signal inserting/branching device, a light signal waveform shaping device, a wavelength converting device and the like composing the optical communication network are generally formed as a device exclusive to bit rate. That is, for example, in order to transmit a light signal of 10 Gbit/s via an optical communication network with bit rate of 2.5 Gbit/s, it is necessary to make some efforts for the system of signal transmission to work.
As one example of such efforts, the following method will be described. That is, in an optical communication network which is designed so as to have bit rate of 2.5 Gbit/s, when a light signal with bit rate of 10 Gbit/s is transmitted, the light signal is branched into four light signals with bit rate of 2.5 Gbit/s, so that the branched signals are transmitted separately. What the light signal with high bit rate is branched so as to be converted into light signals with low bit rate is occasionally called as down-converting.
In order to transmit the branched four light signals individually through an optical transmission path, for example, wavelength multiplex transmission is performed. That is, optical carrier waves with different wavelengths are allocated to the branched light signals with bit rate of 2.5 Gbit/s, respectively, so that the wavelength division multiplex transmission is performed. The light signals are restored to the light signal with bit rate of 10 Gbit/s on a receiving side.
In order to down-convert the light signal with high bit rate so as to transmit it, it is necessary that the branched light signals can be restored to the original light signal with high bit rate on the receiving side. It is necessary to superimpose a control signal requiring for the restoration on the light signal on a transmission side and transmit the superimposed signal. That is, since data such as a control signal to be newly transmitted are added to data of a light signal to be originally transmitted, the total amount of data to be transmitted becomes large. Since transmission signals with low bit rate which are down-converted to be generated arrive with differential time delay on the receiving side, it is necessary to correct the differential time delay between the signals.
According to the method of converting the light signal with high bit rate into the light signals with low bit rate and transmitting them, the control signal for generating the original light signal with high bit rate is also required, and a correcting step or the like for the difference in arrival time of the light signals with low bit rate is required. For this reason, the method of transmission is complicated and the configuration of the device becomes complicated.
In conventional optical communication networks, therefore, light signals are divided according to bit rates, and light relay systems corresponding to the exclusive bit rates are used. Such a process is executed using a communication path control system. That is, systems which are configured of devices which cannot accept changeability of the bit rates of the light signals have basically utilized for the light relay systems in the conventional optical communication networks.
In the future, however, in order to use a limited optical communication path effectively, it is assumed that a system for transmitting light signals with different bit rates through a common optical transmission path would be adopted. In order to realize this, it is assumed that the following communication system would be realized. That is, in optical networks composing future optical communication networks, for example, an information processing unit relating to communication management such as path switching (hereinafter, occasionally called as “management plane”) is realized by an electric unit. Information relating to the bit rates of the light signals propagating through an optical transmission path is input into the management plane in advance. In the management plane, while searching for the information on the bit rate of the light signal propagating through the transmission path, the route of the optical network is switched or configured.
In order to realize the system which is capable of transmitting light signals with different bit rates through a common optical transmission path, it is necessary to introduce not a single bit rate-specific device but a device which can operate for a plurality of bit rates as a light transmitting/receiving device, a route switching device, a light signal inserting/branching device, a light signal waveform shaping device, a wavelength converting device and the like composing the optical communication network.
It is, therefore, an object of the present invention to provide a clock signal extracting method which is capable of extracting a clock signal even if a light signal with any bit rate is received according to a plurality of light signals with different bit rates to be received, and a device which realizes the method.
Concretely, a first object is to provide a method of being capable of extracting a clock signal on a receiving side according to a bit rate notified via a management plane in advance prior to the start of communication, and a device which realizes the method.
A second object is to provide a method of detecting a bit rate of a light signal received on a receiving side and a device which realizes the method.
A third object is to provide a method of being capable of detecting a bit rate of a light signal received on a receiving side and extracting a clock signal according to the bit rate, and a device which realizes the method.